The present invention relates generally to the reclaiming of scrap metal, and more particularly to an improved, efficient reclamation process utilizing hydrocarbon combustibles contaminating the metal.
In the recovery of metals from scrap metal, one of the greatest problems encountered has been the removal of hydrocarbon combustibles, such as oil, paint, grease, and the like, contaminating the metal. Rather elaborate heating processes have been developed to vaporize and remove hydrocarbon contaminants while avoiding oxidation of the desired metal. Oxidation is to be avoided, quite obviously, as such invariably decreases metal recovery. Avoiding oxidation, however, is not so easily accomplished, particularly when reclaiming metal such as aluminum which happens to be particularly troublesome as it tends to oxidize very easily at elevated temperatures. Metal oxidation can be minimized, however, by precise control of process atmospheric conditions. Precise process control can also result in reduced process energy consumption which, in view of today's high energy costs and the energy intensive nature of such processes, is, from an economical standpoint, quite significant.
One process for reclaiming scrap metal and having the same objectives as discussed above is disclosed in U.S. Pat. No. 4,264,060 to Noel H. Twyman. Twyman recognized the economic value of collecting the unburned hydrocarbon vapors emanating from the heated scrap and using them as a supplemental fuel source for heating. In Twyman, the metal scrap is concurrently passed through a rotary kiln with a recycled stream of hot gas. The heated scrap is separated from the gas stream at the discharge end of the kiln and is fed to a melter used to recover the metal. The separated gas stream is then burned and thus heated in an appropriate burner or incinerator, thereby providing the stream of hot gas which is recycled to the rotary kiln for purposes of heating the scrap.
Another scrap metal reclamation process using unburned hydrocarbon fumes as a supplemental source for heating purposes is disclosed in U.S. Pat. No. 3,839,016 to Robert K. Rawlings. The Rawlings process will be discussed in more detail, infra. Both the Rawlings and Twyman processes, however, suffer from process control problems. Both are also unnecessarily complex.